Radioligand-binding analysis of human prostatic alpha-1 adrenoreceptor density following transurethral microwave therapy

Objective To determine the effects of single-session transurethral microwave treatment (TUMT) on human prostatic alpha-1 adrenoreceptor density in patients with symptomatic bladder outlet obstruction caused by benign prostatic hyperplasia. Patients and methods Radioligand-binding assays using H-3-prazosin were performed on prostatic tissue obtained from 25 patients. 10 of whom had received a single TUMT whilst the remaining 15 patients had not, and acted as controls. Prostatic tissue was obtained by cold-punch biopsy immediately before transurethral resection of the prostate from 20 patients 110 following microwave treatment and 10 controls) and from a further five patients at the time of retropubic prostatectomy; these five patients again had undergone TUMT. There were no statistically significant differences in several variables between the groups except for the weight of resected tissue, which was greater for the patients undergoing retropubic prostatectomy. Differences in the maximum receptor density (Bmax) and dissociation constant (Kd) were analysed statistically using the Mann-Whitney U-test because the data were non-parametric. Results Binding was saturable and a single class of high-affinity binding sites was identified in all cases. In the control group, the mean and 95% confidence interval (CI) alpha-1 adrenoreceptor density (Bmax) was 96.4 (82.7-110.1) fmol/mg and the mean (95% CI) dissociation constant (Kd) was 0.56 (0.37-0.74) nmol/L. In those patients who had undergone TUMT, the mean Bmax was significantly lower at 71.3 (58.6-84.7) fmol/mg (P<0.02) but the Kd of 0.56 (0.20-1.14) mmol/L was identical to that in the control group. Conclusions Single-session TUMT, using a non-irrigated catheter, causes a significant reduction in prostatic alpha-1 adrenoreceptor density in the region of the prostate subjected to maximum heating. This may represent one possible mechanism of action by which microwave treatment exerts its beneficial effects.